Wednesday, the US Supreme Court is considering whether an informational checkpoint manned by police on a public road violates the privacy rights of motorists or is an acceptable law enforcement technique in compliance with Fourth Amendment protections.

The case is significant because it is expected to clarify when law-enforcement officials may use roadblocks - including sobriety checkpoints. And it comes at a time when the government is adopting increasingly tight security measures in the on-going war on terrorism.

On one side, civil libertarians argue that citizens must be presumed to be upstanding and are thus entitled to be free from government intrusions, including informational roadside checkpoints. Law enforcement officials and their supporters, however, say such checkpoints are brief, nonadversarial, and benefit the public.

"It is the hallmark of good citizenship to want to help these kinds of investigations," says Gary Feinerman, solicitor general of Illinois, who is urging the high court to uphold roadside checkpoints. "Although there is a minor inconvenience to motorists, most people would understand and appreciate that the police were asking for their help."

Robert Lidster has a different view. In August 1997, Mr. Lidster was arrested at an information checkpoint set up by police in Lombard, Il. The aim of the checkpoint was to locate witnesses to a fatal hit-and-run case a week earlier. But when police smelled alcohol on Lidster's breath and noticed his slurred speech, he was directed to a side street and after further investigation charged with driving under the influence. His DUI conviction was overturned on appeal. The Illinois Supreme Court ruled 4-3 that the roadblock that forced Lidster's interaction with police that night violated his privacy rights.

THE ILLINOIS high court warned that if the information checkpoint in Lombard was upheld by the courts, roadblocks would become a routine part of American life because they could be justified as part of any on-going criminal investigation.

"One of the problems with these so-called interrogational checkpoints is that there is no workable means to prevent their proliferation," says Donald Ramsel, a Wheaton, Il., lawyer representing Lidster.

"If somebody stole a purse inside an office building could police close the office building and force everyone to walk a gantlet and be questioned briefly?," asks Mr. Ramsell. "That would delegate far too much authority [to police]."

The roadblock issue is not new. The high court has authorized the use of roadblocks to search for illegal immigrants near the Mexican border and to carry out DUI checkpoints. In addition, police may use roadblocks in certain emergencies, such as attempts to capture a fleeing dangerous felon, recover a kidnapped child, or thwart an imminent terrorist attack.

But three years ago, in the Supreme Court's last police-checkpoint case, the justices struck down an attempt by officials in Indianapolis to use roadblocks to interdict unlawful drugs. "While we do not limit the purposes that may justify a checkpoint program to any rigid set of categories, we decline to approve a program whose primary purpose is ultimately indistinguishable from the general interest in crime control," wrote Justice Sandra Day O'Connor for the 6-3 majority.

At issue in Wednesday's case, Illinois v. Lidster, is whether police in Lombard set up a valid roadblock. Twenty-three states filed a friend of the court brief supporting Illinois' argument that informational checkpoints should be upheld. In contrast, an estimated 15 states have existing state judicial decisions declaring all roadblocks violate their state constitutions.

"The Supreme Court might be looking to use this case as a platform to indicate that some informational roadblocks are acceptable assuming there are emergency circumstances behind it," says Ramsell. "But our case is what you call a stale crime. There is no emergency, no fleeing felon. This is one week later, the crime is over."

He adds, "If you allow that type of roadblock there would be no ability to prevent the proliferation of roadblocks across America."

Charles Hobson of the Criminal Justice Legal Foundation says courts could limit any potential spread of roadblocks by examining whether they are "reasonable" on a case by case basis.

"Certain suspicionless intrusions are a fact of life," Mr. Hobson says. "They are minimally intrusive and they advance very, very important goals."